Microorganisms belonging to Acetobacter xylinum have been long known as acetic acid bacteria that produce bacterial cellulose. Recently, bacterial cellulose produced by acetic acid bacteria including Acetobacter xylinum has received attention as material for, for example, medical pads or loudspeaker diaphragms because its cellulose microfibrils are more uniformly oriented as compared with plant-derived cellulose so that it is homogeneous and mechanically strong.
However, the cellulose productivity of acetic acid bacteria is low. Therefore, some attempts were made to improve the productivity by varying incubation conditions or introducing mutation. In addition to these conventional means, the modern recombinant gene technology is also being applied in the studies to improve the productivity. In order to bring about gene recombination in cellulose-producing acetic acid bacteria, it is necessary to develop, first of all, a host-vector system for the object bacterium.
It has been known that such microorganisms produce not only cellulose but also acetan which is a water-soluble polysaccharide. In view of the utility of acetan as starting material for food-based thickeners and various chemical products, it is also useful to develop such a host-vector system. Seven vector plasmids carried by Acetobacter aceti subsp. xylinum IFO 3288 were already reported (JPA1-199580).
Plasmids carried by acetic acid bacteria were also reported in JPW4-503456 and Proc. Natl. Acad. Sci. USA, Vol. 87, pp. 8130-8134 (1990).
On the other hand, it would be very convenient for gene recombination of acetic acid bacterial plasmids, if plasmid vectors which can replicate not only in acetic acid bacteria but also other host cells such as E. coli (hereinafter referred to as "shuttle vectors") are available.
Such shuttle vectors were previously reported in, for example, JPA1-199580 cited above and BIOTECHNOLOGY LETTERS, Vol. 14, No. 7 (July, 1922), pp. 539-542.